Third Mass Bleaching

Australia's Great Barrier Reef has suffered its most widespread coral bleaching on record. It is a big threat posed by climate change to the world's largest living organism.

Background:

• Bleaching was first seen on the reef in 1998 -- at the time, the hottest year on record -- but as temperature records continue to tumble its frequency has increased, giving coral less time to recover.
• Back-to-back bleaching events in 2016 and 2017 prompted the government agency overseeing the reef to downgrade its long-term outlook to 'very poor'.
• Aerial analysis conducted by Terry Hughes, director of the ARC Center of Excellence for Coral Reef Studies at James Cook University, and others from the Great Barrier Reef Marine Park Authority, found that coastal reefs along the entire length of the iconic reef -- a stretch of about 1,500 miles (2,300 kilometers) from the Torres Strait in the north, right down to the reef's southern boundary -- have been severely bleached.
• This marks the third mass bleaching eventon the reef in just the last five years and scientists say that the rapid warming of the planet due to human emissions of heat-trapping gases are to blame.

What are coral reefs?

• Coral reefs are some of the most vibrant marine ecosystems on the planet -- between a quarter and one-thirdof all marine species rely on them at some point in their life cycle.
• Often called the ‘rainforest of the seas’—they host an abundant variety of sea life—crucial habitat for about 25% of all ocean species.

Reefs are important because they protect shorelines and coastal regions from erosion and extreme weather events. They are also source of food security for millions of people around the world.

Is coral reef a plant, animal or mineral?

• They look like a plant, but coral reefs are considered animals—they are invertebrates belonging to a group of animals called Cnidaria.
• Other animals in this group include jellyfish and sea anemones.
• Coral reefs are made up of tiny organisms called polyps. The polyps are soft-bodied but secrete limestone skeletons for support.
• Large, iconic reefs are formed when many, many polyps come together and build on one another. The result is a colony of polyps that actually act as one organism.

What is coral bleaching?

• Coral reefs get their colorful hues from algae called zooxanthellae. The coral polyps themselves are actually see-through.
• Polyps and zooxanthellae have a symbiotic relationship, where coral polyps get their food from the algae in exchange for providing housing and protection to the algae.
• When coral get stressed out by things like pollution or high temperatures (often caused by climate change), the coral kick the zooxanthellae out.

No algae=no color=coral bleaching.

• But, it’s a self-defeating response. Corals need the algae for food and to remain healthy—if the coral bleaching goes on for too long, it can actually kill the coral colony.

Why coral reefs are important?

• Food resource: More than 275 million people live within 10 kilometers of coastline and within 30 kilometers of coral. One eighth of the world’s population, approximately 850 million people live within 100 kilometers of coral and are likely to reap the benefits of ecosystem services provided by coral reefs.
• Economic benefits: Coral reefs benefit about 850 million people worldwide, with at least 275 million depending directly on reefs for livelihoods and sustenance.
• A medical future: Coral reefs also contribute to the advancement of research. Reef organisms are used in the treatment of diseases such as certain cancers including leukemia, HIV, cardiovascular diseases, ulcers. In addition, long coral skeleton, because of its very close similarity to our bones nature, served as material for bone grafts.
• Tourism: The reefs attract tourism in effect, freedivers, recreational fishermen and lovers of white sand beaches.  Local economies benefit from billions of dollars from visitors to reefs with their companies exploiting reef ecosystems. Through tourist services, billions of dollars are collected.
• 3-D Habitat: Coral reefs only take up about 1% of the ocean floor, but host an estimated 25% of all ocean species. Coral reefs provide complex, three-dimensional habitat for a huge variety of plants and animals (large and small!), and protect many young fish species as they grow.

What are the mains drivers of coral bleaching?

• Warm ocean temperatures are the main driver of coral bleaching, which is when corals turn white as a stress response to water that is too warm.
  • This happens because they are expelling the algae that grow inside them, which is their main energy source and gives them their color.
  • Bleaching doesn't kill coral immediately. But if temperatures remain high, eventually the coral will die, destroying a natural habitat for many species of marine life.
• Ocean acidification: Coral reefs are being damaged by ocean acidification—which occurs when the ocean absorbs carbon and becomes acidified. Increasing acidification degrades the physical structure of these reefs. This affects all the creatures living among the reef.
• Carbon pollution: Carbon pollution is warming our oceans and causing corals around the world to bleach. It has already led to increased levels of coral bleaching around the world, which are predicted to increase in frequency and severity in the coming decades.

Why is it a concern?

• The bleaching event this year is not only the largest, in terms of the area affected, but also second most severe on record, with the damage likely to be lasting and irreparable.
• In 2016, bleaching killed more than half of the shallow-water corals on the northern region of the Great Barrier Reef. A second mass bleaching in 2017 meant the coral could not recover.
• This year, the cumulative footprint of bleaching has expanded further south, affecting more fragile and heat-sensitive corals.
• As bleaching expands and becomes more frequent, corals are at greater risk of dying off -- and that will be devastating not only for the region's biodiversity, but for the thousands of people whose life and livelihood depend on the reefs.
• Past bleaching events have typically occurred in years with a strong El Nino-Southern Oscillation, a climate phenomena that can increase the odds of a host of extreme weather events around the globe. But as summers get hotter year on year in Australia, scientists found that bleaching can occur even when El Nino is not active. That could have a huge impact on whether the reefs can recover.

Normally, it takes decades for a reef to recover. In that case, what chance do we have for reefs recovering when events are coming back this fast? Though researchers around the world are exploring ways to revive reefs, those efforts will not benefit if the world do not address the root cause of reef’s demise i.e., human caused climate change. The world needs to address climate change to protect coral reefs.